Getting an extra hour of sleep can be the difference between staying healthy and catching a cold, new research confirms.

People who sleep six hours a night or less are more than four times more likely to catch a cold, compared to those who sleep more than seven hours in a night. The new study also shows that even when taking into consideration, age, stress level, race, education, income, or whether or not someone is a smoker, people who get more sleep are better able to fight off a cold.

The findings add to growing evidence emphasizing how important sleep is for health, says lead author Aric Prather, assistant professor of psychiatry at University of California, San Francisco. “It goes beyond feeling groggy or irritable. Not getting enough sleep affects your physical health.”

Prather approached Sheldon Cohen, a psychology professor at Carnegie Mellon University, about the possibility of investigating sleep and susceptibility to colds using data collected in a recent study in which participants wore sensors to get objective, accurate sleep measures.

Cohen’s lab uses the common cold virus to safely test how various factors affect the body’s ability to fight off disease.

Sleep and health

“We had worked with Dr. Prather before and were excited about the opportunity to have an expert in the effects of sleep on health take the lead in addressing this important question,” Cohen says.

For the study, published in the journal Sleep, 164 adults underwent two months of health screenings, interviews, and questionnaires to establish baselines for factors like stress, temperament, and alcohol and cigarette use.

The researchers also tracked their sleep patterns for seven days using a watch-like sensor that measured the duration and quality of sleep throughout the night. Then, the participants were sequestered in a hotel, administered the cold virus via nasal drops, and monitored for a week, collecting daily mucus samples to see if the virus had taken hold.

Subjects who slept less than six hours a night were 4.2 times more likely to catch the cold compared to those who got more than seven hours of sleep, and those who slept less than five hours were 4.5 times more likely.

Sleep carries the day

“Sleep goes beyond all the other factors that were measured,” Prather says. “It didn’t matter how old people were, their stress levels, their race, education, or income. It didn’t matter if they were a smoker. With all those things taken into account, statistically sleep still carried the day and was an overwhelmingly strong predictor for susceptibility to the cold virus.”

The findings show the risks of chronic sleep loss better than typical experiments in which researchers artificially deprive subjects of sleep, because it is based on subjects’ normal sleep behavior. “This could be a typical week for someone during cold season,” Prather says.

The study adds another piece of evidence that sleep should be treated as a crucial pillar of public health, along with diet and exercise, the researchers say. But it’s still a challenge to convince people to get more sleep.

“In our busy culture, there’s still a fair amount of pride about not having to sleep and getting a lot of work done,” Prather says. “We need more studies like this to begin to drive home that sleep is a critical piece to our well-being.”

Other researchers from Carnegie Mellon and from University of Pittsburgh contributed to the study. The National Center for Complementary and Integrative Health, the National Institute of Allergy and Infectious Diseases, the National Heart, Lung, & Blood Institute, and the National Institutes of Health supported the work.